Question

Assume that an X-ray diffraction pattern is taken from two specimens of pure Ni. The two specimens are identical except that one contains numerous twins, while the other is untwinned. Would the XRD patterns show a larger number of diffraction peaks for the specimen containing the twins? Explain the reasoning behind your answer.

Answer 1

Let us assume that ;

1. Specimen with twins ( one type of fracture in crystal) = X
2. Specimen with no twins or untwinned = Y

XRD pattern will be seen if and only if the x-ray diffraction condition is satisfied in particular way.

It shows that,

Which tells that, it depens on d = interplaner spacing of crystal as well as orientation of planes.

For particular in X-type of crystal:

It contains two types of crystal which grew sepearetly in a single crystal. After grwoth it will be seperated by some twin boundary due to which a simple diffraction is problem in such type of crystal. And if you do power xrd you may not seen any changes but if you do single crystal xray it will chages and spots will get splitted. And it will show a less number of diffraction peaks. Because twined crystal is some what mis-oriented crystal so it is less chance for getting satisfactory diffraction condition.

For Y-type of crystal:

It is untwinned, it is better that twin crystal. And you can see better XRD patterns in this type of crystal.